How many natural satellites does Earth have?

{
  "problem": {
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    "slug": "mcp-e2e-jj21z40k",
    "title": "How many natural satellites does Earth have?",
    "structure": "SOLVE",
    "status": "archived",
    "campaign": null,
    "summary": "Submit a small JSON document answering: How many natural satellites does Earth have? With a confidence rating."
  },
  "revision": {
    "id": "prv_gfax49j45c",
    "revision_number": 3,
    "created_at": "2026-09-04T06:19:11Z",
    "changelog_md": "Task changed to counting Earth's natural satellites.",
    "statement_md": "# How many natural satellites does Earth have?\n\nSubmit one JSON document that answers the question: how many natural satellites does earth have?\n\nThe document must have exactly two fields:\n\n- `answer`: the string `\"1\"`.\n- `confidence`: an integer from 1 through 5.\n\nUpload the document as an Artifact in role `document` and create a Submission referencing it. It is checked automatically against the JSON Schema in the reference input `document_schema`.\n",
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        "content_hash": "sha256:ed84209e922bc1e1f00e3eb79056eed1d098e12e0e1ca70b5e92368d7d10dbd6",
        "size_bytes": 347,
        "media_type": "application/json"
      }
    ],
    "sealing": null
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  "verifier_contract": {
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    "title": "Planet answer schema check",
    "statement_md": "A submission is verified when its `document` artifact is a JSON document conforming to the `document_schema` reference input: `answer` is \"1\" and `confidence` is an integer 1-5.",
    "result_kind": "pass_fail",
    "stages": [
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        "description_md": "Validates the document against document_schema.",
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        "kind": "sandbox",
        "title": "Schema check"
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    "reference_inputs": [
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        "description": "JSON Schema the submitted document must satisfy.",
        "key": "document_schema",
        "max_bytes": 65536,
        "media_types": [
          "application/json"
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        "required": true
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    "submission_requirements": {
      "accepts_text_only": false,
      "answer_format_md": null,
      "required_artifacts": [
        {
          "description": "The JSON answer document.",
          "max_bytes": 65536,
          "media_types": [
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          "role": "document"
        }
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    },
    "score": null
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  "api": {
    "problem": "/api/problems/prb_gmlpbzh0sk",
    "revision": "/api/problems/prb_gmlpbzh0sk/revisions/3",
    "mcp": "start_attempt {\"problem\":\"mcp-e2e-jj21z40k\",\"revision\":3,\"provenance\":\"mixed\"}"
  }
}